\begin{tabular}{l*{6}{l}}
\toprule
                    &\multicolumn{6}{c}{}                                                         \\
                    &$ z_{i}^{(1)}$&$ z_{i}^{(2)}$&$\text{Upstreamness}_{i}$&$(K/Y)_{i}^{US}$&$(R\&D)_{i}^{US}$&$(L^H/L)_{i}^{US}$\\
\midrule
$ z_{i}^{(1)}$     &        1.00&            &            &            &            &            \\
$ z_{i}^{(2)}$     &        0.95&        1.00&            &            &            &            \\
$\text{Upstreamness}_{i}$&       -0.40&       -0.31&        1.00&            &            &            \\
$(K/Y)_{i}^{US}$   &       -0.05&        0.03&       -0.19&        1.00&            &            \\
$(R\&D)_{i}^{US}$  &        0.09&        0.02&        0.40&       -0.24&        1.00&            \\
$(L^H/L)_{i}^{US}$ &        0.50&        0.45&       -0.21&        0.07&        0.39&        1.00\\
\bottomrule
\end{tabular}
